Cardiovascular disease is the leading cause of deaths in the industrialized world. Most cardiovascular related deaths are caused by blockage of blood flow in stenotic (narrowed) vessels. The primary cause of narrowing of vessels is the build up of plaque. A common treatment for narrowed blood vessels is deployment of devices like balloon catheters or metallic stents that push the plaque against the wall of the vessel. A commonly used technique for treating coronary artery obstruction is percutaneous transluminal coronary angioplasty (hereinafter referred to as "PTCA") and involves insertion of balloon catheters through the femoral artery to the targeted coronary artery. Injection of radio-opaque contrast into the proximal coronary artery allows fluoroscopic localization of the blocked coronary segments. Balloon catheters are advanced to the site of stenosis over thin guide wires to position the catheter at the point of blockage. The distal end of the catheter contains a balloon which is inflated to press the plaque against the wall of the artery.
A common problem following PTCA is reclosure of the blood vessel. This phenomenon, known as restenosis, is thought to result from intimal hyperplasia of the vessel, in part due to proliferation of smooth muscle cells. Generally, 33%. of balloon angioplasty and metallic stent treatments result in restenosis, which is usually observed within one year of the procedure.
Recently, researchers have begun the use of radiation to inhibit smooth muscle cell proliferation. It has been shown that intracoronary delivery of ionizing radiation causes focal medial fibrosis, which when delivered at the site of the angioplasty, impedes the restenosis process. By carefully selecting the type of radiation, adjacent structures and vessels are undamaged by the radiation.
Currently available devices include radioactive wires or stents, and balloon-less catheters containing radiation pellets. Wire-less, balloon-less radiation pellets have several disadvantages. Centering of the device within the lumen of the vessel is difficult to achieve resulting in delivery of uneven doses of radiation to the entire segment of the vessel wall. These pellets often lay on one side of the vessel and burn that side resulting in necrosis without providing adequate radiation to the other side of the vessel. In addition, there is a danger of loss of pellets from the delivery system. Furthermore, the wire and balloon-less catheter systems also irradiate the entire vessel, even the areas which do not require treatment. Uncontrolled doses of radiation in normal non-stenotic vessels can actually cause proliferation of smooth muscles and other side effects. Radioactive stents and wires that are intended to be left in the vessel for an extended period of time may cause more intimal hyperplasia than ordinary non-irradiated stents. While the radioactive stents and wires may be centered, they are likely to be centered within the off center lumen created by the diseased state rather than the true lumen of the vessel. Again, this may result in uneven delivery of radiation dose to the blood vessel wall.
Thus, there is an ongoing need for devices that can be positioned correctly within the lumen of the blood vessels to reduce the rate of restenosis without major side effects.